1. Field of the Invention
The present invention pertains to ophthalmic diagnosis and therapy, and more particularly, its apparatus, software, means, and methods for diagnosing and treating diseases of the eye. In particular, the present invention provides for improved evaluation of anterior chamber angle by accurately and repeatedly identifying the location of the scleral spur.
The scleral spur is a subtle ridge of the sclera at the level of the limbus interposed between the posterior portion of Schlemm's canal and the anterior part of the ciliary body. The scleral spur is the structure to which some of the ciliary muscle fibers are attached. On cross section, it appears as a hook-like process deep to the scleral venous sinus; relatively rigid, it provides attachment for the meridional fibers of the ciliary body.
Most importantly, this subtle protrusion of the sclera into the anterior chamber is the origin of the longitudinal fibers of the ciliary muscle and is attached anteriorly to the trabecular meshwork. Accurately determining the location of the scleral spur is required in order to determine whether the anterior chamber angle is open, narrow or closed in a particular glaucoma patient. Other established measurements such as angle opening distance and trabecular-iris space area necessitate first identifying the spur.
Thus, the scleral spur is considered the gateway to the anterior chamber and its identification is required for determining whether the anterior chamber angle is open, narrow or closed. The anterior chamber angle, and whether it is open, narrow or closed, is important in determining if any or which medical or surgical interventions should be initiated in a particular patient.
2. Description of the Prior Art
Angle closure glaucoma is a leading cause of blindness, and it is potentially preventable if diagnosed early, before irreversible damage has occurred to the optic nerve.
The current standard for the assessment of anterior chamber angle status is dark-room gonioscopy, in which anterior chamber (iridocorneal) angle is directly visualized. While there is a standardized method of examining, this technique is subjective and a skill that requires that a trained eye specialist identify subtle anatomical structures after placing a lens on the eye while the patient sits in front of a slitlamp, a type of horizontal microscope.
The best way to quantitatively measure the anterior chamber angles and other key parameters is by using anterior chamber imaging approaches such as optical coherence tomography (OCT) or ultrasound biomicroscopy (UBM). Both existing imaging approaches, however, also have shortcomings. OCT is a newer technology which is promising, but cannot effectively image deeper ocular structures. Therefore, the regions behind the iris are not visible to the eye care specialist. UBM allows visualization behind the iris and is useful, but locating the scleral spur is difficult, requiring significant training and experience.
Accurately locating the subtle scleral spur structure with even the highest frequency ultrasound equipment is often difficult and as a consequence the location of the spur must often be estimated.